System, assembly and method for jetting viscous medium onto a substrate

ABSTRACT

System, jetting assembly and method for jetting viscous medium onto a substrate. The system comprises a plurality of ejector devices for jetting individual droplets of viscous medium onto the substrate, a plurality of viscous medium containers for holding and providing the viscous medium to be jetted, at least one holder for holding containers and ejector devices in a jetting machine, and a jetting machine.

This application claims the benefit of U.S. Provisional Application No.60/735/898, filed on 14 Nov. 2005, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present application refers to systems for applying viscous mediumsonto substrates using jet printing within the field of electronicsproduction.

BACKGROUND

Systems, devices and methods for jetting droplets of viscous medium,e.g. solder paste or glue, onto a substrate, e.g. an electronic circuitboard, are known in the art. See for instance International PatentPublications WO 99/64167, WO 00/61297, WO 00/62587, WO 02/05607, WO02/05608, WO 02/32201, WO 02/89545, WO 03/04186, WO 03/51526, WO2004/010753, and WO 2005/048678, which are incorporated herein byreference.

In the MY500 Jet Printer provided by Mydata automation AB, a system forjetting viscous medium comprises a jet printing machine, a solder pastetube for containing solder paste to be jetted, a residue receptacle forholding residue and surplus of solder paste resulting from the jettingprocess, an ejector element for performing the actual jetting of thesolder paste, and a holder matable with the jet printing machine. Theholder, jetting element, residue container, and solder paste tube arearranged to be assembled away from the jet printing machine, and to forman individual, aggregate unit which may be readily positioned in amatable holding elements provided in the jet printing machine. Theejector comprises a feeder in the form of a feed screw, which is poweredby a stepper motor arranged in the holder matable via interface means ofthe stepper motor and the ejector.

SUMMARY OF INVENTIVE EMBODIMENTS

An object of the embodiments presented herein is to provide alternativeor improved systems, assemblies and methods for jetting viscous mediumonto substrates.

For the purposes of this application, it is to be noted that the term“viscous medium” should be interpreted as solder paste, flux, adhesive,conductive adhesive, or any other kind of medium used in connection withthe mounting of components on a substrate, conductive ink, resistivepaste, or the like; that the term “deposit” refers to a connected amountof viscous medium applied at a position on a substrate as a result ofone or more jetted droplets; and that the term “substrate” should beinterpreted as a printed circuit board (PCB), a substrate for ball gridarrays (BGA), chip scale packages (CSP), quad flat packages (QFP),wafers, flip-chips, or the like.

It is also to be noted that the term “jetting” should be interpreted asa non-contact dispensing process that utilizes a fluid jet to form andshoot individual droplets of a viscous medium from a jet nozzle onto asubstrate, as compared to a contact dispensing process, such as “fluidwetting. Furthermore, it should be noted that the individual dropletscan be jetted on at a time, i.e. with an individual trigger thereof.Thus, this is different to the provision of a continuous jet streamwhich is broken into as series of ensuing droplets.

In the following description, inventive embodiments of jetting systemsand methods will be described which comprise a jetting machine, viscousmedium ejectors, viscous medium containers, residue receptacles, andholders. The term “ejector” refers to the element for actuating theactual jetting of viscous medium droplets; “container” refers to theelement in which viscous medium is stored in before and supplied fromduring jetting and is in fluid communication with the ejector;“receptacle” refers to a container for receiving and holding surplus orresidue viscous medium, for instance surplus viscous medium transportedfrom the outlet of the ejector by means of pressurized air; and “holder”refers to a holding frame having mechanical and electrical interfacewith the jetting machine and holds the ejector, container andreceptacle, thus forming an aggregate unit or assembly in conjunctionwith the ejector, container and receptacle, which in the followingdescription will sometimes be referred to as a “cassette”; and “jettingmachine” refers to the framework into which the unit or assembly ismounted. The jetting machine comprises means for holding, positioningand providing trigger signals for the cassettes during the jettingoperation, and also means for holding and transporting the substratesonto which viscous medium is to be applied. The jetting machine furthercomprises software and inspection means for controlling and monitoringthe entire viscous medium application process.

The ejector comprises a jetting nozzle, from where droplets of viscousmedium may be jetted, a feeder, for feeding viscous medium towards thejetting nozzle, and an impactor, i.e. an impacting element for impactingviscous medium fed by the feeder such that droplets of viscous medium isejected through the nozzle. Following an impact on the viscous medium,the impactor is preferably immediately returned to a position ready forimpact, so as to not interfere with the feeding of viscous medium forthe droplet to be subsequently jetted.

The jetting nozzle, in turn, comprises a nozzle outlet through which thedroplets are jetted towards the substrate, said nozzle outlet beinglocated at one end of the nozzle. Furthermore, the nozzle hassurrounding inner walls defining a nozzle space in open communicationwith the nozzle outlet. During jetting operation of the ejector, thenozzle space is filled with viscous medium to a varying degree prior tothe jetting of individual droplets, the degree being adjusted independence on the volume of the droplet to be jetted.

A number of different means or devices for feeding viscous medium areconceivable within the scope of this application, such as pneumaticmeans, gear-driven pumps, piston pumps, etc. However, said feeder is inexemplifying embodiments provided in the form of a rotatable feed screw,for instance such as is disclosed in WO 99/64167.

In the MY500 Jet Printer referred to above, the stepper motor forpowering the feeder of viscous medium within the ejector is provided inthe holder unit. However, according to exemplifying embodiments of thisapplication, a stepper motor, or the like, for powering a feeder mayalternatively be provided in the ejector unit. Thereby, interface meansbetween the holder and the ejector for interfacing the feeder and feederdriving means can be omitted.

According to embodiments of a method and system for jetting viscousmedium, the jetting system comprises a number of differently configuredejectors for use in the same jet printing machine. According toexemplifying embodiments, the ejectors could be adapted to provide aspecific range in terms of the size of jetted droplets, or to specificcharacteristics or properties of the viscous medium. For instance, inone embodiment, the jetting system can comprise a plurality ofdifferently formed ejector types adapted for jetting extra-fine to finesized droplets, fine to medium sized droplets, and medium to large sizeddroplets, respectively. Then, the dimensions of the feeder, impactor andnozzle may be adapted to a particular droplet size range.

In other embodiments, the jetting system can comprise a plurality ofdifferently formed ejector types adapted for jetting, for instance,solder paste, conductive adhesive, glue, and resistive paste,respectively. Moreover, within each different type of medium, such assolder paste, the properties may differ such that different ejectors maybe adapted to, for instance, particular types or ranges of solderpastes. Also, it may be desirable to separate ejectors used for thejetting of viscous medium containing lead from ejectors used for thejetting of lead-free medium.

Furthermore, in further embodiments, the system comprises ejector typesadapted to different combinations of the above examples, i.e. relatingto both different droplet sizes and different viscous mediumcharacteristics.

According to embodiments in which the jetting system comprises aplurality of differently configured ejectors, the jetting machine isadaptable to the different configurations of the ejectors, whenrequired. For instance, in a situation where it is determined that aparticular sized droplet is to be jetted by the ejector, the controlsoftware of the jetting machine may adapt the control signals forcontrolling the feeding of viscous medium into the nozzle and possiblythe impacting thereof by the impactor to the dimensions orcharacteristics of the ejector components. In other words, in an ejectordimensioned for fine to medium sized droplets, the nozzle may have to befully filled with viscous medium before a medium sized droplet can beejected, while in an ejector dimensioned for medium to large sizeddroplets, the nozzle may only have to be half-filled before a mediumsized droplet can be ejected. Thus, the jetting machine, or the softwarethereof, may adapt the control of the jetting process in adaptation tothe particular ejector provided. However, this requires that knowledgeof ejector type and characteristics is provided to jetting processcontrol circuitry.

Furthermore, in embodiments comprising ejectors having differentcharacteristics, the ejectors comprise information elements foridentifying the specific type of ejector. In one example, theinformation element merely provides an identification of the particularejector specimen, i.e. a serial number or the like. However, thisrequires knowledge of the characteristics or ejector type for thatparticular specimen to be known by the control system. Alternatively,the ejectors can comprise information elements not only identifying theparticular specimen, but also the ejector type or even the particularcharacteristics of that ejector type. Such information elements may beprovided as machine readable information elements, preferably such thata jetting machine may more or less automatically read from, and possiblywrite to, the information elements when mounted in the jetting machine,or placed in a vicinity thereof. Furthermore, the information elementsare suitably readable by other equipment used by a circuit boardmanufacturer, such as for registering shipment and arrival of newejectors, for storage and inventory purposes, for preparing subsequentjetting processes and lining up job-queues, etc.

According to exemplifying embodiments, the information element is in theform of an electronic memory circuit provided on or in the ejector.Then, the ejector comprises an electronic interface for communicatingwith the jetting machine, either directly or via separate interfacingelements. For instance, electronic interfaces could be provided in theholder, as defined above, such that electronic connection between thejetting machine and the electronic circuit of the ejector is provided bymounting the ejector in the holder and the holder in the jettingmachine.

Furthermore, embodiments are contemplated in which Radio FrequencyIdentification (RFID) is used for marking and identification ofdifferent ejectors and ejector types. RFID is an automaticidentification method, relying on storing and remotely retrieving datausing RFID tags or transponders. RFID tags contain antennas to enablethem to receive and respond to radio-frequency queries from an RFIDtransceiver. In these embodiments, passive RFID tags are preferably usedas said information elements, requiring no internal power source, whichare provided on the surface of or in the ejector. Then, RFIDtransceivers for communicating with, i.e. reading, the RFID tags areprovided in the jetting machines for identifying the ejectors andejector types.

In other embodiments, the information elements could be in the form ofbar code labels, or the like, provided on an external surface of theejector. Then, a bar code reader is preferably provided at or in thejetting machine.

Furthermore, the information elements referred to above could holdinformation of further properties of the ejectors, either via theidentity of the particular specimen or as direct information held by theinformation elements. Examples of such further properties could includenumber of jetted droplets, manufacturing dates, time of latest ejecteddroplet, etc.

In further embodiments, a visual marking is provided on the ejector inorder to provide an easily discernible indication of the ejector typefor an operator. The visual marking could be in the form of a colormarking, for instance provided as a label on a surface of the ejector,or as a coloring provided on all or a portion of the ejector surface.The visual marking could also, or alternatively, be in the form of asymbol, number or character indicating the ejector type, or provided asa pattern on a label on the ejector surface. Of course, the colors,symbols and patterns could be combined in order to further enhance thedistinguishing effect, for instance to mitigate problems relating tooperators suffering from color blindness or numeric dyslexia.

It should be noted that for embodiments having visual markings providedon the ejectors, the ejectors could also be provided with bar codelabels, electronic memory circuits, or RFID tags, etc.

According to further embodiments, the jetting system could furthercomprise a number of viscous medium containers, i.e. for containing theviscous medium to be jetted in the jetting machine, holding differenttypes of viscous mediums or similar type of viscous medium withdifferent properties or characteristics. A further alternative could beto provide containers having different configurations, for instance inadaptation to the contained amount of viscous medium or othercharacteristics of the medium. Then, the containers could compriseinformation elements holding information related to characteristics ofthe container or of the contents thereof. For example, the informationelements provided on or in the container can hold information of thetube specimen, type of container, type of viscous medium, the initialfilling amount or degree, batch identity, best-before date, type ofejector (for which the container is intended to be used), etc.

There is a considerable advantage in providing these informationelements in machine-readable form and not just as text on a label. Anexample of such an advantage is that a jetting machine can provideinformation about the containers to an operator, e.g. a warning that thebest-before date has already passed for a particular containers. Also,the batch identity of the viscous medium can be stored together withother production data for future traceability. Furthermore, if eachcontainer is provided with a unique identity, then the machine cannotice if the container has been replaced since the cassette was lastused and take any appropriate action. One example of such an actioncould be to jet a sufficient amount of viscous medium in order to ensurethat any air introduced when replacing the container is expelled fromthe cassette.

In the same manner as stated above in relation to the ejectors, theinformation elements of the containers could for instance be in the formof memory circuits, bar code markings, or RFID tags. Since thecontainers are intended for holding articles of consumption, use ispreferably made of low-cost information elements, such as bar codelabels and RFID tags. Thereby, the containers could be designed asdisposable items while maintaining a reasonable manufacturing cost.

The RFID tags are further advantageous in that they are not sensitive toa particular orientation of the tag. On the contrary, an RFID tag couldbe read by a transceiver located in the vicinity of the RFID tag,regardless of the particular orientations of the tag. This is incontrast to the bar code label, which requires a certain proximity to abar code reader, as well as an orientation which enables the reading ofthe bar code.

Furthermore, the containers could be provided with visual markings forproviding an easily discernible indication of the type of container orcontainer content for an operator. As stated above in relation to theembodiments of differently configured ejectors, the visual marking couldbe in the form of color markings, for instance provided as a label on asurface of the container, or as a coloring provided on all or a portionof the container surface. The visual marking could also, oralternatively, be in the form of a symbol, number or characterindicating the type or content of the container, or provided as apattern on a label on the container surface.

According to embodiments where differently configured ejectors areadapted for jetting of different media, there can be provided visualmarkings on the ejectors which correspond to visual markings provided onthe containers. As an example, ejectors intended and adapted for jettingconductive glue of a certain type can be provided with a color markingof the same color as the color marking on a container holding conductiveglue. Thereby, an operator can very easily select an ejector suitablefor jetting medium from a particular container, i.e. with a particulartype of medium.

Furthermore, the corresponding visual marking of the ejector and thecontainer could be related to the mechanical interface between theinteracting elements. Thus, in order to speed up the process for anoperator in combining a container with an ejector having a matchingmechanical interface, the container and ejector are for instance colorcoded to provide the indication of their association and enabledassembly.

Moreover, in further embodiments, the mechanical interface per se can bearranged for distinguishing between matching or associated containersand ejectors. In other words, differing mechanical interfaces can beused for preventing a container holding a particular viscous medium tobe connected with an ejector not adapted to jetting that particularmedium. As an example, ejectors to be used for jetting of lead-freesolder pastes could be provided with a mechanical interface that is onlyconnectable to containers holding lead-free solder paste and having acorresponding mechanical interface.

Preferably, the containers are generally in the form of syringe typetubes or cartridges. However, it should be noted that any other suitableshapes and forms of viscous medium containers and cartridges can be usedwithout departing from the scope of this application.

As mentioned above, the system also comprises residue receptacles forreceiving and holding surplus and residual viscous medium, such asviscous medium residue removed from the nozzle outlet in order to avoidsuch residue from interfering with the jetting process and negativelyaffecting jetting accuracy. Generally, the viscous medium residue isremoved from the nozzle by providing an air flow passed the nozzle andinto the receptacle. The receptacle comprises an inlet for receiving theviscous medium, the inlet suitably facing the area surrounding thenozzle outlet, a chamber for holding the viscous medium, and a filterallowing the flow of air to pass through the receptacle, whilepreventing viscous medium from escaping the receptacle with the flow. Amore detailed description of such receptacles can be found in WO02/89545, the contents of which is incorporated herein by reference. Thereceptacles can be provided as disposable items, i.e. to be used onlyonce, but the scope of the present application also includesnon-disposable receptacles, i.e. arranged as a multiple-use article.

According to exemplifying embodiments, the receptacle comprises couplingelements for mechanically interfacing the ejector, the viscous mediumcontainer, and/or the holder. Therefore, in embodiments in which thejetting system comprises differently configured ejectors and/orcontainers, the system can also comprise differently configuredreceptacles adapted to the configurations of the ejectors or containers.Furthermore, the size of the receptacles could be adapted to the size ofthe container, such that a smaller receptacle is adapted and intendedfor use with a smaller viscous medium container.

In a manner similar to that stated above in relation to containers andejectors having differing configurations or properties anddistinguishing therebetween, the receptacles may be provided withmachine readable information elements, such as bar codes, RFID tags, andelectronic memory circuits holding information on properties andcharacteristics of the receptacle. Furthermore, the receptacle can beprovided with easily discernible visual markings of the type referred toabove, such that an operator easily may combine a particular containerand/or ejector with a suitable type of receptacle. The examples givenabove for identification, information and markings of ejectors andviscous medium containers, and the properties and contents thereof, arealso conceivable for the embodiments of different types of receptacles.

As mentioned to some extent above, the holder is intended forconstituting a mechanical interface between the jetting machine, on theone hand, and the ejector, container and receptacle, on the other hand.Thus, the jetting system according to embodiments thereof can comprise anumber of differently configured holders adapted for interfacing andinteracting with differently configured ejectors, viscous mediumcontainers and residue receptacles. For instance, the holders can beadapted to the sizes of the containers in order to facilitate theprovision of a steady and reliable mechanical coupling between theholder and the container, which in turn increases the accuracy of thejetting process.

As understood by the skilled person, the holders can be provided withmachine readable information elements, in a manner similar to the abovedescription in connection with the distinguishing between differentlyconfigured containers, receptacles and ejectors, respectively. Thus, thealternatives of machine readable information elements, such as barcodes, RFID tags, and electronic memory circuits holding information onproperties and characteristics of the carrier, also applies for theholders. Preferably, a readable and writable electronic memory circuitwill be provided as said information element, since the holder comprisesan electronic interface with the jetting machine. Furthermore, theholder will most likely not be manufactured as a disposable article.

Also, the holder can be provided with easily discernible visual markingsof the type referred to above, such that an operator easily may combinea selected ejector and a selected container with a corresponding holder.The examples given above for identification, information and markings ofejectors and viscous medium containers, and the properties and contentsthereof, are also conceivable for the embodiments of different types ofholders.

Furthermore, according to exemplifying embodiments of this application,the holders in the jetting system can also be provided with informationelements for providing a unique holder identity. Thereby, a jettingmachine can identify holder-ejector combinations that has previouslybeen inserted and calibrated in the machine. The term “calibrated” inthis context refers to jetting a plurality of droplets from theejector-holder combination, preferably onto a calibration surface,evaluating the results of said jetting, e.g. by measuring the positionof the resulting deposits, and adjusting jetting parameters such astrigger timing and positioning on the basis of the evaluation. A moredetailed description of a calibration procedure is disclosed in WO02/32201, which is incorporated herein by reference. Thus, even thoughthe holder may have been used with other ejectors, and possibly also inother jetting machines, the identity of the holder and the ejector canbe determined by the jetting machine. Thereby, the results of a previouscalibration process with that particular holder-ejector combination canbe retrieved and, at least partly, re-used. If the ejector-holderassembly has not been separated since the latest use thereof, there is ahigh probability that the prior calibration results are still correctand can be fully re-used.

In the embodiments described above, the four elements of ejector,holder, container and receptacle are presented as being separateelements that are attachable for use in a jetting process, and separablewhen located away from the jetting machine. A major advantage of such asolution resides in the fact that if a malfunctioning should occur, e.g.due to wear, it will generally only be necessary to replace a singleelement. This would include the receptacle being prematurely filled withviscous medium residue, i.e. before the container runs out of viscousmedium. However, as will be discussed in the embodiments disclosedbelow, these basic elements may be combined for use as integral unitsthat are not intended to be separated.

Firstly, the ejector and the holder may be combined as a separate,integral unit. This would entail a number of advantages, in addition tothe obvious advantage of enabling the number of information elements andvisual markings to be reduced. For instance, a number of mechanical andelectrical interface elements that are required for assembling theseparate ejector and holder in the known jetting system may of course beomitted when providing the ejector and holder as an integral unit. Forinstance, if a feed screw is used as a feeder, the stepper motor can bearranged in the same unit as the feeder, which would reduce the numberof interacting elements and, hence, manufacturing costs.

Furthermore, repeated assembling and disassembling of mating parts mayprovide a non-negligible strain and wear on interfacing elements. Byomitting the requirement of assembling and disassembling the ejector toand from the holder, the wear on the ejector and holder may be reduced,thus enhancing the working life of the ejector-holder combination.

Secondly, the viscous medium container and the ejector may be providedas a separate, integral unit. Then, the number of required informationelements and visual markings for identification and distinguishingbetween different types of ejectors and containers may of course bereduced. Also, the advantage of avoiding a number of interfacingelements also applies for this combination, even though there typicallywill not be an electrical interface between the ejector and thecontainer. However, by providing the ejector and container as anintegral unit, the problem of selecting a suitable ejector and containercombination is completely eliminated. For instance, there is no longerany risk of an operator mistakenly selecting an ejector which previouslyhas been used with one medium, which may have left residue in theejector, for assembling and jetting of medium from a container holding adifferent medium.

Furthermore, by providing the ejector-container as one integral unit, aresulting integral viscous medium passageway from the container portionof the integral unit to the ejector portion thereof may be arranged.Thereby, there will be no risk of contamination of the viscous mediumfrom foreign substances, which otherwise could be a problem if theassembly of separate ejector and container elements is not performed ina clean area environment. In other words, the risk of an operatorbringing any of the respective interfaces of a separated viscous mediumpassageway into contact with foreign substances, which in turn couldhave a detrimental effect on the jetting operation, is completelyeliminated by providing the ejector-container combination as an integralunit.

Moreover, in some embodiments, the ejector-container combination can bearranged as a disposable unit.

Thirdly, the container and the receptacle may be provided as an integralunit. This enables the omission of interfacing elements between these toelements, having the advantages of reducing manufacturing costs, etc. Italso enables the design and dimensions of the receptacle to be adaptedto the viscous medium type and volume since there is no doubt with whichcontainer the receptacle is to be used. Thereby, the receptacles can bemade smaller when integrated with a smaller container, and the overalldimensions of the aggregate cassette may be reduced.

Furthermore, the container-receptacle combination can be manufactured asa disposable unit. Then, the receptacle is preferably made from alow-cost material, such as plastic.

Also, according to exemplifying embodiments, the ejector and thereceptacle can be provided as an integral unit. Interfaces between theejector and the receptacle can be omitted, and interfaces between thecontainer and both the ejector and the receptacle can limited to oneinterface between the container and the integral ejector-receptacleunit. Thus, manufacturing and assembly of the different elements can besimplified, and the wear between otherwise required interface elementseliminated, which would enhance working life of the elements and reducemanufacturing costs.

As understood by the skilled person, the embodiments of having anintegral receptacle-container combination could also be combined withthe embodiments of having integral holder-ejector units andejector-container units, respectively. Thus, embodiments arecontemplated where the jetting system comprises two separate units formounting and interacting in a jetting machine, an integralholder-ejector unit to be assembled with an integralcontainer-receptacle unit, and a holder to be assembled with an integralcontainer-receptacle-ejector unit.

According to further embodiments related to visual markings of ejectors,holders, containers, and/or receptacles, there may be provided a palletof visually distinguishable labels, stickers or tag. Then, the operatorcan use similar labels for associating separate elements to be usedtogether in the future. As an example, an operator may have a pluralityof similar ejectors at his disposal, and a jetting process for jetting,for instance, solder paste and conductive glue. Then, the operator mayallocate some ejectors for jetting solder paste and some for jettingglue, select suitable labels, and attach similar labels to the gluecontainers and glue ejectors, and other labels to the solder pastecontainers and solder paste ejectors, respectively. Thereby, an improvedend-user flexibility is provided in associating separate elements, andvisually indicating the different associations.

Even though the inventive embodiments has been described above usingexamples thereof, alterations, modifications, and combinations thereof,as understood by those skilled in the art, may be made without departingfrom the scope of this application. For instance, the above describedembodiments and examples relating to the particular parts of the jettingsystem, i.e. to the ejector, holder, container, and receptacle,respectively, are contemplated to be combined in any conceivable manner.Even though each possible combination have not been explicitly statedherein, such conceivable combinations are intended to be comprised inthe application. Furthermore, as readily understood by the skilledperson, the parts of the jetting system as described above comprisefurther elements that have not been mentioned or described above.However, the omission of such elements must not be taken in a limitingsense.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES OF DRAWINGS

FIG. 1 is a perspective view showing the general outline of a apparatusfor application of solder paste according to exemplifying embodiments;

FIGS. 2 a and 2 b are perspective views of an embodiment of a jettingassembly shown in both separated and assembled state;

FIG. 3 is a perspective view of an aggregated viscous medium containerand viscous medium receptacle;

FIG. 4 is a sectional view of an embodiment of a jetting assemblyshowing a portion of an ejector and a receptacle according toexemplifying embodiments;

FIG. 5 is an alternative sectional view of the embodiment shown in FIG.4;

FIG. 6 is an enlarged sectional view of the embodiment of FIG. 4 showinga portion thereof in greater detail; and

FIG. 7 is an enlarged sectional view illustrating the flow path at thejetting outlet of the embodiment shown in FIG. 4.

DESCRIPTION OF EXEMPLARY EMBODIMENT

FIG. 1 illustrates the general outline of a preferred embodiment of anapparatus 1 for providing a substrate (not shown) with deposits bydispensing droplets of a viscous medium onto the substrate, i.e.jetting, in accordance with the embodiments disclosed in the presentapplication. For ease of description, the viscous medium willhereinafter be referred to as solder paste, which is one of thealternatives defined above. For the same reason, the substrate will bereferred to as an electric circuit board and the gas will be referred toas air. In the following, a jetting assembly will be depicted as anassembly of separate elements including a holder, an ejector, areceptacle and a container. However, as described above, the separateelements can be combined in several combinations to form an integralunit, respectively, making up part of the assembly. Thus, the ejectorand the holder may be combined as a separate, integral unit; the viscousmedium container and the ejector may be provided as a separate, integralunit; the container and the receptacle may be provided as an integralunit, the ejector and the receptacle can be provided as an integralunit; and the container, the receptacle, and the ejector can be providedas a separate, integral unit. All these stated combinations arecontemplated for the purposes of this application, although not all areexplicitly shown in the figures or described in detail below.

In the described embodiments, the jetting apparatus or machine 1 is of atype comprising an X-beam 3 and an X-wagon 4, which is connected to theX-beam 3 via an X-rail 10 and is movable in a reciprocating way alongthe X-rail 10. The X-beam 3, in turn, is movably connected to a Y-rail2, the X-beam 3 thereby being movable to the X-rail 10. The Y-rail 2 isrigidly mounted in the jetting apparatus 1. Generally, the movements areprovided by linear motors (not shown).

Furthermore, the jetting apparatus 1 comprises an internal conveyor 7for carrying the board through the jetting apparatus 1, and a lockingdevice for locking the board when jetting is to take place.

A docking device is attached to the X-wagon 4 for enabling releasablemounting of an assembly 5 at the docking device. The assembly 5 isarranged for dispensing droplets of solder paste, i.e. jetting, whichimpact and form deposits on the board. The jetting apparatus 1 alsocomprises at least one vision device, e.g. a camera. The camera is usedfor determining the position and rotation of the substrate or board andfor checking the result of the dispensing process by viewing thedeposits on the board. Furthermore, a cassette calibration unit 9 and acamera calibration unit 8 are provided for calibration of the jettingapparatus.

Additionally, the jetting apparatus 1 comprises a vacuum ejector 6(schematically shown in FIG. 5) arranged on the X-wagon 4, and a sourceof compressed air (not shown). The vacuum ejector, as well as the sourceof compressed air, is in communication with the docking device via airconduit interface means which are connectable to complementary airconduit interface means, of the docking device.

As readily understood by those skilled in the art, the jetting apparatusalso comprises a processor or control unit 80 (schematically shown inFIG. 5) for executing software running the apparatus.

Briefly, the jetting apparatus works as follows. The board is fed intothe jetting apparatus 1 by means of the conveyor 7, upon which the boardis placed. When the board is in the correct position under the X-wagon4, the board is fixed with the aid of the locking device. By means ofthe camera, fiducial markers are located, which markers are prearrangedon the surface of the board and used to determine the precise positionthereof. Then, by moving the X-wagon over the board in a predetermined(pre-programmed) pattern and operating the jetting assembly 5 atpredefined locations, solder paste is applied on the board at thedesired locations.

With reference to FIGS. 2 a, 2 b and 3, an exemplifying embodiment of ajetting assembly 5 will now be described in more detail. In FIG. 2, theassembly 5 is illustrated in an exploded view showing its separateelements, as well as when assembled in the form of an aggregate unit.The jetting assembly 5 comprises an assembly holder 11 having holdingmeans 12 for connecting the jetting assembly 5 to an assembly support ofthe docking device, as well as a holding element 13 for securing theassembly of the aggregate unit 5. Furthermore, in this embodiment thejetting assembly 5 comprises a viscous medium container 14 providing asupply of solder paste, and a viscous medium receptacle 15 for receivingviscous medium residue produced during the jetting operation. Thejetting assembly 5 is connected to the vacuum ejector 6 and the sourceof pressurised air via a pneumatic interface 50, which will be furtherillustrated below. Furthermore, the assembly 5 comprises a jettingdevice or ejector 16, as well as a motor unit 17 provided for drivingthe feeding, i.e. a rotatable feed screw 32, of viscous medium into aneject chamber 28 of the jetting device 16. In this embodiment, the motorunit 17 is pivotally mounted to the holder 11, such that the motor unitmay be folded away for providing easy assembly of the assembly element,which is illustrated in the exploded view of FIG. 2.

Also, in FIG. 3, the container 14 and the receptacle 15 are shown as anaggregate unit separate from the ejector 16, the motor unit 17 and theholder 11. In this embodiment, the container 14 and receptacle 15 areassembled prior to mounting them into the holder 11 for forming theassembly 5. Preferably, the receptacle 15 and the container 14 aredelivered to the manufacturing site as an already assembled unit, to bemounted with the holder 11, ejector 16 and motor unit 17 to form theassembly 5 for performing the jetting operation.

With further reference to FIGS. 4-7, the contents and function of thedevice enclosed in the jetting assembly 5 will be explained in greaterdetail. As can be seen in these sectional views, the jetting assembly 5includes a ejector or jetting device 16 comprising an actuator lockingscrew 20 for supporting an actuator, and a piezoelectric actuator 21formed by a number of thin, piezoelectric elements stacked together toform the actuator 21, which is rigidly connected to the locking screw20. The jetting device 16 further comprises a bushing 25 rigidlyconnected to a housing 19, and a plunger 23 rigidly connected to the endof the piezoelectric actuator 21, opposite the position of the lockingscrew 20. The plunger 23 is axially movable while slidably extendingthrough a bore in the bushing 25. Cup springs 24 are provided toresiliently balance the plunger 23 against the housing 19, and forproviding a preload for the actuator 21. An eject control unit (notshown) applies a drive voltage intermittently to the piezoelectricactuator 21, thereby causing an intermittent extension thereof and hencea reciprocating movement of the plunger with respect to the housing 19,in accordance with solder pattern printing data.

Further, the jetting device comprises an eject nozzle 26 operativelydirected against the board 2, onto which small droplets of solder pasteare to be jetted. In the nozzle 26, there is comprised a jetting orifice27 through which the droplets are jetted. The surfaces of the nozzle 26surrounding the jetting orifice 27 and facing the substrate 2 will bereferred to as a jetting outlet. The plunger 23 comprises a pistonportion which is slidably and axially movably extending through a pistonbore 35, an end surface of said piston portion of the plunger 23 beingarranged close to said nozzle 26. An eject chamber 28 is defined by theshape of the end surface of said plunger 23, the inner diameter of thebushing 25 and the nozzle orifice 27. Axial movement of the plunger 23towards the nozzle 26, said movement being caused by the intermittentextension of the piezoelectric actuator 21, will cause a rapid decreasein the volume of the eject chamber 28 and thus a rapid pressurisationand jetting through the nozzle orifice 27, of any solder paste containedin the eject chamber 28.

Solder paste is supplied to the chamber from the supply container 14,see FIG. 2, via a feeding device. The feeding device comprises anelectric motor, arranged in the motor unit 17, having a motor shaft 29partly provided in a tubular bore 30, which extends through the housing19 to an outlet 36 communicating via a tubular bore 31 with said pistonbore 35. An end portion of the motor shaft 29 forms a rotatable feedscrew 32 which is provided in, and coaxial with, the tubular bore 30. Anessential portion of the rotatable feed screw 32 is surrounded by anarray of resilient, elastomeric o-rings 33 arranged coaxially therewithin the tubular bore 30, the threads of the rotatable feed screw 32making sliding contact with the innermost surface of the o-rings 33.

The pressurised air obtained from the above-mentioned source ofpressurised air (not shown) is arranged to apply a pressure on thesolder paste contained in the supply container 12, thereby feeding saidsolder paste to an inlet port 34 communicating with the tubular bore 30.An electronic control signal provided by a supply control unit (notshown) to the motor causes the motor shaft 29, and thus the rotatablefeed screw 32, to rotate a desired angle, or at a desired rotationalspeed. Solder paste captured between the threads of the rotatable feedscrew 32 and the inner surface of the o-rings 33 are then made to travelfrom the inlet port 34 to the piston bore 35 via the outlet port 36 andthe tubular bore 31, in accordance with the rotational movement of themotor shaft 29. A sealing o-ring 22 is provided at the top of the pistonbore 35 and the bushing 25, such that any solder paste fed towards thepiston bore 35 is prevented from escaping from the piston bore 35 andpossibly disturbing the action of the plunger 23.

The solder paste is then fed into the eject chamber 28 from an outletport 36 of the tubular bore 30 via the conduit 31 and a channel 37. Thechannel 37 is provided in the piston portion of the plunger 23, whereinsaid channel 37 has a first portion extending axially into said plungerand communicating with the conduit 31, and a second portion extendingcoaxially with and within said plunger 23 from said first portion to theend surface of the plunger facing the eject chamber 28.

As can most clearly be seen in FIG. 6, the jetting device 15 of thejetting assembly 5 comprises a support plate 40 located below ordownstream of the nozzle orifice 27, as seen in the jetting direction.The support plate 40 is provided with a through hole 41, through whichthe jetted droplets may pass without being hindered or negativelyaffected by the support plate 40. Consequently, the hole 41 isconcentric with the nozzle orifice 27.

According to this embodiment, the ejector 16 comprises an air flowpassage 38 consisting of a first portion defined by the nozzle orifice27, the nozzle 26 and the support plate 40, said first portion defininga disc shaped space concentric with the piston bore 35; a second portiondefined by the nozzle 26 and the support plate 40, connected to saidfirst portion and extending coaxially about the nozzle 26; and a thirdportion defined by the housing 19 and the bushing 25, connected to thesecond portion, parallel with the piston bore 35 and extending coaxiallyaround the part of the bushing 25 facing said third portion. The airflow passage 38 is further in communication with an air flow conduit 39located on the side of the piston bore 35 opposite that of the tubularbore 31. The air flow conduit 39 extends from the third portion of theair flow passage 38 and the viscous medium waste container or receptacle15.

Thus, when the assembly 5 is assembled, the receptacle 15 for collectingfragments of residue solder paste will be connected to the ejector 16.The receptacle 15 can be best seen in FIG. 5, where it is schematicallyshown in its entirety. The receptacle 15 is connected to the ejector 16at an interface provided on the ejector 16, via a correspondinginterface 50 arranged on the receptacle 15. The receptacle 15, whichwill be described in more detail below, also provides an interface 51and communication between the jetting assembly 5 and the vacuum ejector6. Thereby, the negative pressure or vacuum produced by the vacuumejector is conveyed to the ejector 5, and to the communicating air flowconduit 39 and airflow passage 38.

The receptacle 15 comprises an air conduit 53, forming an air flow pathor channel within the receptacle 15. The air conduit 53 has a firstportion communicating with said connecting interface 50 and is alignedwith the air flow conduit 39 of the jetting assembly, and a secondportion extending perpendicularly from said first portion. At the endthereof, the air conduit 53 takes the form of a guiding tubing which isin communication with a collection chamber 55, arranged for collectionof solder paste residue removed from the jetting outlet. Preferably, theconduit 53 has an outlet 54 that is directed downwards, thus guiding thecarried solder paste towards the bottom of the chamber. At the top ofthe collection chamber 55, a narrow air conduit 52 leads the air flowout of the collection chamber 55. Thereby, the air will flow from theoutlet 54 of the conduit 53 and deflect into the air conduit 52 at thetop of the collection chamber, while the main portion of the solderpaste residue will be released, due to the momentum thereof and gravity,from the air stream and fall into the collection chamber.

Even if the majority of collected solder paste residue carried by theair flow is released and collected in the collection chamber, a smallportion thereof may still be carried onwards by the air flow. Therefore,the receptacle further comprises a filter 57, into which said narrow airconduit guides the flow of air. The filter 57 is of conventional typeand provided for preventing any fragments of solder paste not collectedin the collection chamber 55 from reaching the vacuum ejector. Thefilter is arranged in a longitudinal bore 56 and is in communicationwith an outlet conduit 58, in communication with the outlet interface 51provided for interface with the vacuum ejector 6.

The receptacle 15 is releasably connected to the vacuum ejector 6, ofconventional type, which is arranged for evacuating the receptacle 15.The vacuum ejector 6 is connected to the receptacle 15 via the airoutlet 58, a connector 60 and an air tube 61. Even though the vacuumejector is illustrated as being separate from the solder paste ejector16 and/or the receptacle 15, a number of other placements orcombinations of the vacuum ejector 6, the ejector 16, and the receptacle15 are of course conceivable within the scope of the embodimentspresented in the present application. However, the vacuum ejector 6, theconnector 61 and the air tube 61 are preferably arranged in the jettingmachine 1, i.e. separate from the elements making up the jettingassembly 5.

Furthermore, a flow sensor 70 is arranged and positioned in the air tube61. The flow sensor is arranged for measuring the air flow in the airflow path of the jetting apparatus, i.e. including the air flow conduit39 and air flow passage 38 of the ejector; the conduit 53, thecollection space 55, the narrow air conduit 52, the filter 57, and theoutlet conduit 58 of the receptacle 15; as well as the connector 60 andthe air tube 61. Use can be made of any available flow meter suitablefor the particular flow range and having a suitable size for positioningand measuring in the flow path of the air tube 61, for instance the MEMSMass Flow Sensor provided by Omron Electronic Components Europe B.V.

The flow sensor 70 is electronically connected to he control unit 80,which is also arranged for receiving and evaluating the measurementsignal 71 output by the flow sensor.

In operation, the vacuum ejector 6 evacuates the waste container 15,including evacuation of the air conduit 53, the collection space 55, thenarrow air conduit 52, the filter 57, the outlet conduit 58, theconnector 60 and the air tube 61. This evacuation produces an air flowthrough the waste container as indicated by the arrows in FIG. 5. As aconsequence, air flow conduit 39 and air flow passage 38 of the ejector16 are also evacuated via their interface. Thus, air is sucked inthrough the outlet hole 41, which gives rise to a strong air flow in adirection reverse to that of the jetted droplets. This air flow willpass the jetting outlet and remove any undesired residue of solder pastethat may have become adhered to the jetting outlet, for reasonsdescribed above.

According to the preferred embodiments, the air flow is continuouslyprovided before, during and after the jetting of each droplet. Also, theair flow could be provided intermittently, following a predeterminedtime period of jetting, or following a predetermined number of jetteddroplets. It is also contemplated that the accumulation or build-up ofsolder paste residue at the jetting outlet is monitored, and that theflow of air is provided when the accumulation reaches a certain level.However, it is preferred that the air flow is constantly provided duringthe jetting process.

Thus, the air will flow through the air flow passage 38 and continueinto the receptacle 15 via the air flow conduit 39. Due to the force ofthe air flow, solder paste fragments removed from the vicinity of thejetting outlet will be transported or carried through the air flowpassage 38, the air flow conduit 39 and into the receptacle 15. Insidethe receptacle 15, the air will flow through the air conduit 53 and intothe collection chamber 55. Due to the force of gravity, the majority ofthe solder paste residue transported by the air flow will fall into thecollection chamber 55, while the air flow will continue into the narrowconduit 52. Any residue of solder paste that may continue along with theair flow into the narrow conduit 52, will be collected by the filter 57,thus preventing fragments of solder paste from reaching the outletconduit 58.

Furthermore, as the jetted droplets face a strong head wind immediatelyfollowing the jetting thereof, any droplets having a jetting trajectorywith an angular deviation from that intended, will encounter a slightside wind. The effect of the side wind on a jetted droplet will bedependent of the magnitude of angular deviation. As a consequence, theangular deviation can be enhanced to such an extent that the jetteddroplet will “miss” the hole 41 and instead be collected by the supportplate 40. The above may also be the case for any satellites, describedabove, which due to their angular deviation will encounter a side windand be collected by the support plate 40. Then, the air flow present orlater produced in the air flow passage will transport away any solderpaste collected by the support plate 40. Due to the lower velocity andsignificantly smaller volume of the satellites, as compared to thesolder paste droplets, the satellites will be much more prone to beaffected by the side wind.

The preceding specific examples are illustrative of the embodiments ofthe present application. It is to be understood, therefore, that otherexpedients known to those of skill in the art or disclosed herein may beemployed without departing from the invention as defined by the appendedclaims. It is therefore understood that the embodiments may be practicedotherwise than what is specifically described herein without departingfrom the scope of the present application.

1. A system for jetting viscous medium onto a substrate, comprising: aplurality of ejector devices for jetting individual droplets of viscousmedium onto the substrate, a plurality of viscous medium containers forholding and providing the viscous medium to be jetted, a receptacle forreceiving and collecting viscous medium residue produced during saidjetting of individual droplets, at least one holder for holdingcontainers and ejector devices in a jetting machine, and a jettingmachine.
 2. An assembly for jetting viscous medium onto a substrate,comprising: an ejector device for jetting individual droplets of viscousmedium onto the substrate, a viscous medium container for holding andproviding the viscous medium to be jetted, a receptacle for receivingand collecting viscous medium residue produced during said jetting ofindividual droplets, and a holder for holding said ejector device,viscous medium container and receptacle as one aggregate unit.
 3. Amethod of jetting viscous medium onto a substrate, comprising the stepsof: providing an ejector device for jetting individual droplets ofviscous medium onto the substrate, providing a viscous medium containerfor holding and providing the viscous medium to be jetted, providing areceptacle for receiving and collecting viscous medium residue producedduring said jetting of individual droplets, providing a holder forholding said ejector device, viscous medium container and receptacle asone aggregate unit, assembling said aggregate unit, mounting said unitin a jetting machine, and jetting droplets of viscous medium onto asubstrate.